An example of such a system is described in the above-identified related application, the contents of which are incorporated herein by reference.
However, the aforementioned system is primarily concerned with "front end" processing, i.e. the actual raster scanning of the article under test to produce a video signal, and the processing of the video signal to provide a binary signal S in which at least one selected image feature is represented by a first logic level and non-selected features and background are represented by a second logic level. The actual comparison techniques which may be used do not form a central part of the related application.
By contrast, it is an object of the present invention to provide a particular comparison technique which can operate in real time using both a binary signal of the type such as the aforesaid signal S derived by scanning the article under test (but not necessarily derived in the specific manner described in the above identified related application), together with image information concerning the master article previously stored in at least two storage means.